1. Field of the Invention
The present invention relates to an ultra low power thermally-actuated oscillator, in particular to an oscillator in which only a current with low power consumption is required to be applied to produce deformation of a line-structured thermally-actuated element, which drives the proof masses of the oscillator to produce the corresponding harmonic oscillation.
2. Description of the Related Art
Micro-electro-mechanical systems oscillators (MEMS oscillators) can generally be categorized into three types, i.e., capacitive, piezoelectric and thermal-piezoresistive, and each has its advantages and disadvantages respectively. The capacitive oscillator may provide low power, high mechanical quality factor (Q) in vacuum and good IC compatibility, but it suffers from poor linear effect and complicated manufacturing process, and requires a larger transduction area and a tiny capacitor gap, such that the Q of the resonator is low in the atmosphere and the frequency response of the resonator is easily interfered by the parasitic capacitance so that the ratio of signal to background feedthrough signal is low, and the phase change is small. The piezoelectric oscillator has an extremely high electromechanical coupling coefficient, so that the motional impedance is low, but it has disadvantages of low Q, for example, the manufacturing process of the substrate materials is difficult to be integrated with the CMOS process. Therefore, the application of the piezoelectric oscillator is also limited.
The thermally-actuated oscillator converts heat energy into a driving force. The manufacturing process thereof is simple and only one to two photo masks are required, as compared to those of the capacitive and piezoelectric oscillators which require the large sensing area or tiny capacitor gap. Furthermore, the compatibility with the CMOS manufacturing process is high because the MEMS structural material is silicon, the resonator still has a considerable Q in the atmosphere, and self-sustained oscillation by using thermal, mechanical, electrical coupling effects inside its structure is feasible. Currently, the lowest operational power for oscillators recorded in the literature is about a few mW.